The present invention relates to a device for measuring by means of light rays, for example a distance-measuring device, with a reduced share of stray light.
Measuring devices that use a light ray, such as laser beams, to for example measure the distance between the measuring device and an object of interest, are well known. In such devices a light beam is sent in the visible or invisible range, such as a laser beam, through a lens array and a share of the light beam reflected by the object passes through the lens array again and is received by a detector of the measuring device. From the received signal, the distance of the measuring device to the object can be derived, for example through measurement of path time or phase measurement of the emitted light signal to the received light signal.
Such known devices for measurement employing a light beam usually use the optical lens array do not merely send and receive the light signal for distance measurement, for example, but also use the lens array as an optical device for searching for and aligning the device to the object of interest. For this purpose, an eyepiece can be made available to the user, or a sensor for generating an image on a screen.
One distance-measuring device is known from US 2006/0114448. In this distance-measuring device, a prism is connected to a lens array, to couple laterally emitted light into an optical axis. The mirror or prism is placed in the central area of the lens array on the optical axis. Measurement light reflected from an object is collimated by the lens array and directed to a detector that preferably lies in the focus of the array. Since the detector, viewed optically, is behind the coupled prism, not all the light that is reflected from the object reaches the detector array. The detector can receive only such light reflected from the object as usable light, which is incident through the optical lens array and past the prism to the detector.
Due to placement of the prism in the optical path of the lens array and because the prism is designed to be small, to permit as much measurement light as possible to be incident on the receiver, especially when the measurement light is coupled into the optical path through the mirror or prism, crosstalk effects result, which impair the quality of the measured result. Stray light or reflected light generated in the measuring device by the light beam can be incident on the receiver as stray light, and impair the ratio of usable light to stray light.
In the process of overall technical development it is desirable to be able to measure greater distances to the object, and thus use light sources with greater power output. With a higher power class, for example with a stronger laser, stray light also becomes greater and the precision of the measured result is determined by the ratio of usable light to stray light. Therefore, in such devices with a greater power class, the dynamic range must be expanded. When distance is measured, the stray light is included, and thus, for example, when usable light undergoes a fourfold amplification if a higher power class for example is used, stray light is increased by a factor of 4, which does not increase the dynamic range, i.e., the distance from usable light to stray light.